Eh, it’s very cumbersome. I’ve not been able to do a full one arm hanging leg raise, I always get my legs to the L then it’s like I can’t activate my shoulder properly or something. The actual core strength is probably pretty similar to a two arm hanging leg raise, the difficulty comes in with the shoulder. Grip shouldn’t be too bad because if you’re strong enough to do a one arm leg raise then hanging from the bar with one arm should be easy.
If any of that is incorrect I’m sure Al will be able to correct me, seeing as he can actually do that exercise haha.
If you’re just looking for something harder than hanging leg raises to use as a ‘standard’ exercise, I would recommend developing the dragon flag, V sit, qnd/or stand to stand bridge. These skills are all great goals but will also build strength that is very applicable to other advanced skills. Any lever training would also be good (back lever, human flag, planche…).